I work for Garmin and have been beta testing the Nav V for the past month.
I can guarantee you it isn't based on the Montana.

Did you guys fix the Bluetooth stereo music (A2DP) quality? I paid $1000 for this thing (Nav IV) based on the idea that I'd be able to listen to music through my helmet. Apparently the BT chip is grossly under-spec'ed for A2DP which unsurprisingly results in in extremely poor quality for music. Music requires a substantially higher bitrate than the phone/voice-guidance features. Currently have to use my cell phone for music listening purposes, the Nav IV is "unlistenable".

I have tested this with three Nav IVs and a 660 with eight different bluetooth headsets, all sound horrid. Most noticeable on the higher frequency sounds where digital over-compression is the most catastrophic, but it does a fine job of ruining the other frequencies as well.

My tested headsets include several Sena SMH-10s, Cardo Scala Rider G4, Cardo SRC system for Schuberth C3, Motorola S9-HD, Sony MW600. Navigator IV/Zumo 660 have been tested with every firmware version to current (4.80). I think I tried versions as low as 3.50. (I tried very, very, hard to correct this problem, your technical support had no answers). I have taken music from CD and sampled it with multiple MP3 encoders at bitrates ranging from 128kbps to 320kbps, have tried VBR and fixed bitrates on the music.

Please simply fit a bluetooth chip comparable to that found in any given modern smartphone to correct this problem. I do software development for mobile phones, and have never seen Bluetooth quality anywhere close to this bad on any of the dozens of phones I've tested my software on. This includes the cheap $100 pay-as-you-go items.